A tilt (tilt angle) is often given to a radio wave (beam) emitted from a base-station antenna device serving as one type of antenna device. For example, a downward tilt angle is generally given to a radio wave emitted from a base-station antenna device for a mobile phone. This is because the radio wave emitted from the base-station antenna device needs to be prevented from reaching the outside of an area (cell) assigned to this base-station antenna device. U.S. Pat. No. 5,940,030 (Patent Document 1) discloses one example of a phase shift circuit for giving the tilt angle to a radio wave emitted from an antenna device including a base-station antenna device.
The phase shift circuit disclosed in the Patent Document 1 is provided with a signal line, opposing ground conductors with the signal line interposed therebetween, and a dielectric plate that is inserted in a gap between the signal line and the ground conductor. The dielectric plate is inserted in the above-mentioned gap from a direction perpendicular to an extending direction of the signal line, and is overlapped with the signal line. In the following description, the extending direction of the signal line is referred to as “line length direction”, and the direction perpendicular to the extending direction of the signal line is referred to as “line width direction”. More specifically, the dielectric plate is inserted in the gap between the signal line and the ground conductor from the line width direction, and is overlapped with the signal line.
The Patent Document 1 describes that, when the amount by which the signal line and the dielectric plate are overlapped with each other, that is, an overlapped area between the signal line and the dielectric plate is varied, the phase of a signal output from the signal line is changed, with the result that the tilt angle of a radio wave emitted from the antenna device is changed.